1. Field of Invention
The invention relates to systems and methods for providing a compensation factor for a registration system that takes into account differing physical characteristics of. various substrates used in the system. In particular, a compensation factor, such as an empirically or theoretically derived effective drive roll radius, is stored for various substrates and used in drive roll control profile computations to provide process direction registration and velocity control of the substrates passing through the system.
2. Description of Related Art
There are a variety of transport and registration systems in use that transport and register various substrates, such as copy sheets. In many registration systems, such as those often found in copiers, facsimiles, and printers, drive mechanisms often include at least one driven elastomer-covered roll backed by a hard idler roll to form a roll pair defining a nip region therebetween. A substrate, such as copy paper, provided to the nip region is advanced by rotation of the roll pair, specifically rotation of the driven roll, which causes corresponding linear movement of the substrate, such as paper.
High quality documents require registration of sheets to a photoreceptive surface for image transfer. In order to achieve this, accurate registration control is needed to locate the sheet with respect to the image. Conventional machines use various types of sheet registration devices. Some sense the position of the sheet at a first location and use this sensed information to generate a set of control signals to cause the sheet to arrive at a second location in proper registry. Other systems compute or approximate sheet position indirectly based on known parameters of the registration system and sensed values of various drive elements.
In most conventional registration systems used for printers, copiers and facsimile machines, the types of substrates being transported usually do not vary much. That is. many systems typically encounter only a limited number of different substrate types, such as basic draft sheet stock of a certain weight in basic sizes such as A4 or 8.5xc3x9711 inches. A typical registration system is designed to transport, for example, 20 lb. bond sheet stock (roughly 75 grams/m2 or GSM). Occasionally, higher quality bond paper of a slightly higher weight, such as 24 lb. bond (roughly 90 GSM) or 28 lb. bond (roughly 105 GSM) sheet stock is used. In conventional registration systems, these sheets are transported using the same drive profiles. That is, the drive control parameters are fixed (i.e., set irregardless of the weight of the sheet being used).
In conventional drive roll systems, angular velocity and degrees of rotation of the driven roll can be readily determined from conventional measurement systems, such as rotary encoders, or can be assumed to be known from the control parameters sent to the motor (as in stepper motor drive systems). From this information and knowledge of the roll radius of the drive roll, the system can, through equations, approximate the linear movement of the substrate passing through the nip region. This linear movement, including travel velocity, is relevant because various timing and other position control factors are based on the determined linear velocity of the substrate. For example, if it is desired that a substrate reach a desired position such as a leading edge transfer position 1000 mm from the drive roll at a given time t, through computation knowing both the distance (1000 mm) and the determined linear velocity (X mm/sec), the time to start the transport can be calculated. Alternatively, or in addition thereto, a desired velocity can be set to match other system components so that the substrate is desired at a select location at a desired speed and at a desired time based on the determined linear velocity.
In the United States, paperweight is expressed as pounds per 500 sheet ream of uncut C-size paper (4xc3x97 letters size). As such, a cut ream of 20 pound letter paper (500 sheets of 8.5xc3x9711) would weigh 5 pounds. Because each type of paper has a different basis size, it is often confusing to talk in terms of the U.S. pound weight system. Instead, it is much more convenient to express paper xe2x80x9cweightxe2x80x9d as mass per unit area as in the ISO (metric) system In which the weight of paper Is given in grams per square meter (GSM). For example, 20 pound bond letter stock corresponds to roughly 75 GSM, 24 pound bond letter stock corresponds to roughly 90 GSM, and 28 pound bond letter stock corresponds to roughly 105 GSM. 20 pound Bristol board on the other hand, which has a different basis size, corresponds to roughly 44 GSM. Other known substrates can have substantially higher GSM, some over 300 GSM.
While prior printers, copiers and facsimile machines typically encountered only a handful of different types of substrates, such as A4 or 8.5xc3x9711xe2x80x3 papers in only a small range of paper weights or densities, today there is a trend toward using more and more diverse varieties of substrates in such systems. Registration systems today thus may be required to accommodate delivery of a wide variety of substrates, each having diverse physical properties.
An exemplary system according to the invention is expected to support substrates between about 49 to 280 GSM (grams/m2). However, the physics involved in transporting such substrates through a nip region results in slightly differing linear movement of the substrate given the same drive control profile for the drive roll that is driving the substrate. That is, it has been found that differing physical properties, such as, for example, substrate thickness, substrate stiffness, substrate mass per unit area, substrate coefficient of friction to the driven roll, and the like cause a variance in actual linear transport displacement and speed with a given fixed drive roll displacement and speed profile. Because the assumed linear speed of the substrate is used to control the registration system, Applicant has found that if there is no compensation for the variations in actual travel displacement and speed due to the physical differences in substrates being transported, the final registration and velocity of the substrate will vary correspondingly as the assumed displacement and velocity deviates from actual linear displacement and velocity.
Moreover, such variances in velocity may cause speed mismatches with other system components, causing undesirable effects on the substrate such as image quality defects, jams, or the like. As printing resolutions are becoming increasingly smaller, system tolerances have become similarly increasingly small. Accordingly, even seemingly small deviations may have intolerable effects on the resultant print system registration.
Because of this, there is a need for a method and system that can compensate the drive profile of the registration system to account for such deviations due to delivery of different substrates.
There also is a need to compensate for arrival time differences and/or substrate speed differences due to the use of substrates with different physical properties.
Exemplary systems and methods of the invention achieve this by providing a lookup table or other predefined compensation factor that accounts for differences in one or more physical properties of substrates being transported and registered so that the registration system will reliably register substrates, regardless of such differences in physical properties.
Exemplary systems of the invention may include at least one roll pair formed by a first, driven roll and a second roll defining a nip therebetween that is part of the transport path through which a substrate is passed. A lookup table including a compensation factor for plural different kinds of substrates is prestored, with each compensation factor being based on physical characteristics of the substrate that impact velocity of the substrate along the transport path. A particularly relevant compensation factor is an effective drive roll radius. A substrate determination device, such as an input from the operator of the system or an automatic detection system, determines the substrate being transported. A registration controller operably connected to the first roll controls a drive profile of the first roll. The drive profile is compensated by the compensation factor to adjust the drive profile to correspond to the specific substrate being transported.
Exemplary methods according to the invention may include: receiving an input selecting one of a variety of different substrate types to be registered by a registration system; accessing a prestored compensation factor corresponding to the selected substrate type that includes at least an effective drive roll radius based on at least the mass per unit area of the selected substrate type; adjusting the drive profile of the roll pair based on the obtained compensation factor; and driving the roll pair using the compensated drive profile.